This research is a seismic performance study of un-reinforced brick masonry residential buildings in Peshawar region. Seismic performance study of the structural system of a locality includes (i) investigation of the seismic demand to which the structure is subjected, and (ii) determination of seismic resistance of structures under existing field practice.
Seismic demand on structures in a particular area is most commonly determined from seismic risk maps of that area. In light of locally available data, attenuation relationships, seismic intensity scales, geology, tectonics, earthquake history and review of the published work on the relevant topic, a revised seismic risk zoning has been suggested for Peshawar region. This corresponds to zone-2b of the UBC seismic risk zoning and to 0.16g in terms of Peak Ground Acceleration (PGA). Based on the revised seismic risk zoning, design spectrum has also been constructed for use in seismic demand studies on structures located in the city, using the software Strong Motion Analyzer (SMA), developed as part of this study. The software is capable of plotting response time histories from ground motion records for any damping ratio and period, response spectra corresponding to various damping ratios and design spectra based on the Newmark’s model.
To determine seismic resistance of brick masonry buildings built under current field practice in the area under study, a number of standard tests on brick unit, mortar and brick mortar assemblage were carried out in the laboratory. Besides lab tests, a dynamic field test was also carried out on full scale single story brick masonry structure. The model structure was erected in actual ground conditions and simulated earthquake vibrations were produced through controlled underground explosions, specially designed for this purpose. Based on masonry properties accrued from lab and field tests, Finite element models of the brickwork system were also studied. The combination of experimental and numerical study thus led to various valuable results pertaining to behavior of masonry structural systems.
To evaluate demand/capacity ratio and hence to identify potential weak zones in a structure, another software named Shear Damage Index (SDI) has also been developed. The software plots contours of the demand/capacity ratio for a structure numerically modeled, and, identifies the weak zones as the zones where the ratio exceeds one. The software uses the analysis output results of the finite elements model and user defined resistance values for comparison.
One of the major findings of the research include that masonry dwellings of the locality constructed with 9 inch walls having cement based mortars in the proportion of 1:6 with fine aggregates as sand, Khaka (stone dust) or their combination will mostly remain intact under the seismic demand experienced in the locality.